Recently the applications of two-dimensional (2D) materials have been broadened by engineering their mechanical, electronic, and optical properties through either lateral or vertical hybridization. Along with this line, we report the successful design and fabrication of a novel triphasic 2D material by vertically stacking lateral 2H-/1T'-molybdenum disulfide (MoS 2) heterostructures on graphene with the assistance of supercritical carbon dioxide. This triphasic structure is experimentally shown to significantly enhance the photocurrent densities for hydrogen evolution reactions. First-principles theoretical analyses reveal that the improved photoresponse should be ascribed to the beneficial band alignments of the triphasic heterostructure. More specifically, electrons can efficiently hop to the 1T'-MoS 2 phase via the highly conductive graphene layer as a result of their strong vertical interfacial electronic coupling. Subsequently, the electrons acquired on the 1T'-MoS 2 phase are exploited to fill the photoholes on the photo-excited 2H-MoS 2 phase through the lateral heterojunction structure, thereby suppressing the recombination process of the photo-induced charge carriers on the 2H-MoS 2 phase. This novel triphasic concept promises to open a new avenue to widen the molecular design of 2D hybrid materials for photonics-based energy conversion applications.

@article{osti_1356943,
title = {Triphasic 2D Materials by Vertically Stacking Laterally Heterostructured 2H-/1T'-MoS2 on Graphene for Enhanced Photoresponse},
author = {Cui, Weili and Xu, Shanshan S. and Yan, Bo and Guo, Zhihua H. and Xu, Qun and Sumpter, Bobby G. and Huang, Jingsong S. and Yin, Shiwei W. and Zhao, Huijun J. and Wang, Yun},
abstractNote = {Recently the applications of two-dimensional (2D) materials have been broadened by engineering their mechanical, electronic, and optical properties through either lateral or vertical hybridization. Along with this line, we report the successful design and fabrication of a novel triphasic 2D material by vertically stacking lateral 2H-/1T'-molybdenum disulfide (MoS2) heterostructures on graphene with the assistance of supercritical carbon dioxide. This triphasic structure is experimentally shown to significantly enhance the photocurrent densities for hydrogen evolution reactions. First-principles theoretical analyses reveal that the improved photoresponse should be ascribed to the beneficial band alignments of the triphasic heterostructure. More specifically, electrons can efficiently hop to the 1T'-MoS2 phase via the highly conductive graphene layer as a result of their strong vertical interfacial electronic coupling. Subsequently, the electrons acquired on the 1T'-MoS2 phase are exploited to fill the photoholes on the photo-excited 2H-MoS2 phase through the lateral heterojunction structure, thereby suppressing the recombination process of the photo-induced charge carriers on the 2H-MoS2 phase. This novel triphasic concept promises to open a new avenue to widen the molecular design of 2D hybrid materials for photonics-based energy conversion applications.},
doi = {10.1002/aelm.201700024},
journal = {Advanced Electronic Materials},
number = ,
volume = 3,
place = {United States},
year = {2017},
month = {5}
}

In this paper, the electronic properties of MoS 2 are strongly controlled by the structure, providing a route to their modulation. We report, based on first principles calculations, that the adsorption of metal atom Cu on the surface can induce the phase transition of MoS 2 from the semiconducting 2H to the metallic 1T' phase. Cu adsorption results in effective n-type doping of MoS 2 by charge transfer from Cu in the case of the 1T' phase. This is distinct from the behavior in the 2H phase, where Cu does not donate any charge, and it is also distinct frommore » alkali metal adsorption, where charge is donated to both 2H and 1T' MoS 2. Charge donation to the 1T' phase by Cu stabilizes it with respect to the 2H structure and importantly, it also reduces the energy barrier between the 2H and 1T' structures. This difference reflects the higher electronegativity of Cu, which also indicates that Cu-modified MoS 2 can be expected to be less chemically reactive than MoS 2 with alkali metal adatoms. The main atomic mechanism of the structural transition is the gliding of S atoms on the upper surface. Finally, we report the energetics of the 2H to 1T' transition with several other adatoms, Ag, Au, Ni, Pt and Pd, but none of them are as effective as Cu in inducing the transition.« less

In this work, results for the adhesion energy of graphene and MoS 2 to silicon based and metal substrates using the intercalation of nanoparticles method are presented. In this method, nanoparticles are dispersed onto the substrates before transferring the 2D material onto the substrate. This causes a blister to form, the width and height of which can be measured by AFM. Using a simple model then allows for the adhesion energy to be found. The substrates tested are SiO 2, Si 3N 4, gold, and platinum. Gold is found to have the highest adhesion energy per area of 7687.10 andmore » 1207.26mJm -2 for graphene and MoS 2 respectively.« less

The high-yield and scalable production of single-layer ternary transition metal dichalcogenide nanosheets with ≈66% of metallic 1T phase, including MoS 2xSe 2(1-x) and Mo xW 1-xS 2 is here achieved via electrochemical Li-intercalation and the exfoliation method. Thin film MoS 2xSe 2(1-x) nanosheets drop-cast on a fluorine-doped tin oxide substrate are used as an efficient electrocatalyst on the counter electrode for the tri-iodide reduction in a dye-sensitized solar cell.

Based on density functional theory, we have investigated the electronic properties of molybdenum disulfide-niobium disulfide hybrid nanoribbons (MoS{sub 2}-NbS{sub 2} NRs). It is found that the MoS{sub 2} edge, MoS{sub 2} center, NbS{sub 2} edge, and NbS{sub 2} center have distinct contributions to the collective electronic behaviors of MoS{sub 2}-NbS{sub 2} NRs. Its behavior, metallic or semiconductor, depends on whether the central area of NR contains NbS{sub 2} chain or not. This dependence has been also revealed in the electronic structures of NbS{sub 2}-MoS{sub 2}-NbS{sub 2} NR and MoS{sub 2}-NbS{sub 2}-MoS{sub 2} NR, of which the former is semiconductor andmore » the latter is metal. In comparison with MoS{sub 2} NR of the same width, the hybrid has a different bandgap that was caused by the coupled effects between NbS{sub 2} edge and MoS{sub 2} edge. This fact makes MoS{sub 2}-NbS{sub 2} NRs a possible candidate for nanoelectronic devices based on heterostructured transition-metal dichalcogenide.« less